Speaker
Description
Compact supermassive dark-matter (DM) states act as gravitational lenses. Widely spatially separated space-based gamma-ray detectors would observe geometrical parallax of such an intervening lens with respect to cosmologically distant gamma-ray bursts (GRB). This parallax can be of order the Einstein angle of the lens, resulting in a significant differential magnification of the source as viewed from the two detectors. Simultaneous brightness measurements of the same GRB made by two detectors can therefore detect or exclude such DM states. Recent studies have shown that this "picolensing" signal could be a promising way to search in particular for primordial black hole (PBH) dark matter in part of the "asteroid mass window", roughly $10^{-15} < M_{\text{PBH}}/ M_{\odot} < 10^{-10}$. In this talk, I will discuss my work to explore the robustness of this signal to various uncertainties not previously carefully accounted for: most importantly, to uncertainties in the transverse extent of the observed GRB emission region. I'll show that, while large GRB source-size uncertainties do degrade previous projections somewhat, it is still possible to probe most of the PBH DM asteroid mass window with a future mission that employs two Swift/BAT-class detectors separated by a distance on the order of an AU. Depending on the total number of GRBs that such a mission ultimately observes, it may even be possible to robustly probe new subcomponent DM parameter space at PBH masses above the window, potentially as high as $2 \times 10^{-8} M_{\odot}$. Time permitting, I will also discuss recent work to extend this observable to the detection of spatially extended dark lenses, such as QCD axion miniclusters.